The present invention generally relates to the manufacture of tools used in processes for die cutting sheet-type work material, and is more specifically directed to a method of fabricating said tools such that said die cut work material can be advanced thereon without becoming caught.
In general, product packages, boxes, and the like are fabricated from die cut blanks made from sheet-type work material. Usually the blanks take the form of the product package or box in its unfolded or flat condition. To create a finished blank, a sheet of work material is advanced to several different processing stations, each performing a different work operation on the material. For example, the work material is initially advanced to a cutting station where a die-board having a series of rules projecting therefrom, is brought into engagement with the sheet of work material, usually cardboard.
In general, the rules are arranged in a pattern conforming to the shape of the blank to be cut, as well as to any internal areal sections to be cut from the blank, as well as any scrap material to be removed. In addition to the rules that cut through the work material, some are positioned such that when they engage the work material, they form indentations therein corresponding to crease lines in the blank.
During the die cutting operation, a series of small sections of work material, referred to by those skilled in the die cutting art as xe2x80x9cnicksxe2x80x9d. bridge the gaps between the cut blank, and the remainder of the sheet of work material. The nicks prevent the blank from separating from the sheet of work material, which may have several blanks cut thereon, thereby allowing the sheet to be advanced to the next work station. Nicks also prevent any areal sections of work material corresponding to cut-outs in the blank from separating therefrom.
Subsequent to the die-cutting operation, the sheet of work material is usually advanced to a tool referred to by those in the art as a stripping board, where the areal sections corresponding to the cut-outs in the blank and any scrap material are removed. As used herein, the term xe2x80x9ctoolxe2x80x9d should be broadly construed to include stripping boards, blanking tools, and their components. The stripping board typically consists of a female stripping board and a mating male stripping tool. The female stripping board has cut out sections therein that match the cut outs in the female stripping board. The male stripping tool includes protrusions projecting outwardly therefrom, of a shape complimentary to the cut outs in the female stripping board.
During operation, the sheet of work material having the blank retained thereon by the nicks, is advanced onto the female stripping board. The male stripping tool is then brought into engagement with the work material, thereby breaking the nicks and pushing the cut outs from the work material, through the corresponding cut outs in the female stripping board.
In some cases, subsequent to the above described stripping operation, the work material is advanced onto a blanking tool. Similar to the stripping board, the blanking tool includes a female tool having a cut out therein conforming to the shape of the outer periphery of the blank. The blanking tool also includes male tool having a portion projecting outwardly therefrom of a shape complimentary to the cut out in the female tool.
During a blanking operation, the male tool engages the sheet of work material, breaking the nicks retaining the blank thereon, thereby separating the blank from the sheet of work material. In both the stripping and blanking operations, it is desirable that the edges defined by the peripheries of the cut outs in the female stripping tool, and the female blanking tool be as sharp as possible in order to insure that the nicks are cleanly broken and that the edges of the blank and the cut outs therein are not torn, crushed, or otherwise deformed.
However, a problem associated with the edges of the cutouts in the female stripping board and blanking tool often occurs. Once the blank is die cut and held to the sheet of work material by the nicks, the blank(s) tend to sag away from the sheet of work material. Therefore, as the work material is advanced onto either the female stripping board or the female blanking tool, the edges of the blank, and the cut outs therein have a tendency to catch on the edges defined by the female stripping board and the female blanking tool, potentially damaging the blanks and disrupting the production thereof.
In an effort to address the problem of the blank edges catching on the tool, the edges defined by the tools have been chamfered or otherwise relieved. Historically, the process of chamfering the edges of the female stripping boards and the female blanking tools, has been accomplished using a hand held router. This often results in more material than is necessary being removed on more edges than are necessary to prevent the advancing work material from catching. Accordingly, when the stripping and blanking operations are performed, the relieved edges on the tools causes the edges in the blank to become crushed or otherwise deformed. This manual operation is time consuming and largely dependent on the operator""s skill.
Based on the foregoing, it is the general object of the present invention to provide a method for preventing the advancing work material from catching on the stripping and blanking tools that overcomes the problems and drawbacks of prior art methods.
It is a more specific object of the present invention to provide a method for relieving the edges defined by the stripping and blanking tools that results in minimum material removal on the tools, and deformation of the blank.
The present invention is directed to a method for selectively relieving sharp edges in tools used in die cutting web, or sheet-type work material wherein a machining apparatus is provided and includes a rotary cutter movably mounted thereon. The tool is supported on the machining apparatus with the rotary cutter being moveable relative to the tool. The tools can each be of a different shape and include a variety of cut outs, each having a different shape. Accordingly, a controller is associated with the machining apparatus and has machine readable shape data corresponding to the configuration of at least one of the tools, stored therein.
The controller is programmed to determine, responsive to the shape data stored therein, the locations of edge segments defined by the tool against which the work material will impinge as it is advanced in a known direction onto the tool. The controller then generates a machining path which when followed by the cutter will relieve only those edge segments against which the work material will impinge as it is advanced.
In the preferred embodiment of the present invention, the cutter is a rotary implement, such as, but not limited to a router bit. The tool generally includes at least one, and more often several cut outs or apertures. The machining path generated by the controller is defined in part by a path approximately equivalent to the shape of the aperture, shifted by a predetermined distance. Preferably, the predetermined distance relative to the aperture is approximately one half of an effective cutting diameter defined by the rotary cutter in the direction at which the work material will be advanced onto the tool. This predetermined distance defines the edge of the relief to be machined into the female stripping board. The term xe2x80x9ceffective cutting diameterxe2x80x9d should be broadly construed herein to mean the diameter of the rotary cutter at a point equivalent to the desired depth of the relief cut to be made.
In addition to the above-described apertures, the tools usually include at least one outer edge that will be encountered by the advancing work material. Often these outer edges are shaped such that portions thereof are parallel to the direction of work material advancement while others are perpendicular or oriented at some other angle relative to the direction of work material advancement.
This being the case, the shape data stored in the controller includes data corresponding to the shape of the outer edges of the tool that will be encountered by the advancing work material. Accordingly, the machining path generated by the controller is defined in part by a path approximately equivalent to the shape of the outer edges shifted by approximately one half of the effective cutting diameter of the rotary cutter in the direction at which the work material will be advanced onto the tool.
One advantage of the present invention is that the above described machining path results in relieving only those edges that have the potential to interfere with the advancement of the work material. For Example, edges parallel to the direction of advancement of the work material would not be machined. Nor would the edges of a shaped opening that are trailing relative to the direction of the advancing work material.
Another advantage of the present invention is that the above described method of relieving sharp edges results in minimal material removal. For example, where an edge is inclined relative to the direction of advancing work material, the edge would be proportionally smaller than it would be for an edge that is perpendicular to the advancing work material. In addition, where the edge to be relieved is arcuate, the relief will be crescent-shaped relative to the direction of advancement of the work material.